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Tilman
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/* Copyright (c) 2006 Google Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package sample.gbase.basic;
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import org.xml.sax.Attributes;
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import org.xml.sax.SAXException;
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import org.xml.sax.helpers.DefaultHandler;
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import java.io.IOException;
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import java.io.InputStream;
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import java.net.HttpURLConnection;
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import java.net.URL;
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import java.net.URLEncoder;
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import java.util.Stack;
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import javax.xml.parsers.ParserConfigurationException;
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import javax.xml.parsers.SAXParser;
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import javax.xml.parsers.SAXParserFactory;
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/**
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* Display the titles of the Google Base items that match a specific query.
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*/
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public class QueryExample2 {
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/**
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* Url of the Google Base data API snippet feed.
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*/
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private static final String SNIPPETS_FEED = "http://base.google.com/base/feeds/snippets";
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/**
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* The query that is sent over to the Google Base data API server.
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*/
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private static final String QUERY = "cars [item type : products]";
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/**
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* Create a <code>QueryExample2</code> instance and
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* call <code>displayItems</code>.
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*/
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public static void main(String[] args) throws IOException, SAXException,
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ParserConfigurationException {
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new QueryExample2().displayItems();
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}
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/**
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* Connect to the Google Base data API server, retrieve the items that match
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* <code>QUERY</code> and call <code>DisplayTitlesHandler</code> to extract
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* and display the titles from the XML response.
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*/
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public void displayItems() throws IOException, SAXException,
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ParserConfigurationException {
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/*
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* Create a URL object, open an Http connection on it and get the input
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* stream that reads the Http response.
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*/
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URL url = new URL(SNIPPETS_FEED + "?bq=" +
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URLEncoder.encode(QUERY, "UTF-8"));
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HttpURLConnection httpConnection = (HttpURLConnection) url.openConnection();
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InputStream inputStream = httpConnection.getInputStream();
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/*
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* Create a SAX XML parser and pass in the input stream to the parser.
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* The parser will use DisplayTitleHandler to extract the titles from the
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* XML stream.
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*/
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SAXParserFactory factory = SAXParserFactory.newInstance();
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SAXParser parser = factory.newSAXParser();
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parser.parse(inputStream, new DisplayTitlesHandler());
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}
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/**
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* Simple SAX event handler, which prints out the titles of all entries in the
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* Atom response feed.
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*/
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private static class DisplayTitlesHandler extends DefaultHandler {
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/**
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* Stack containing the opening XML tags of the response.
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*/
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private Stack<String> xmlTags = new Stack<String>();
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/**
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* Counter that keeps track of the currently parsed item.
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*/
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private int itemNo = 0;
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/**
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* True if we are inside of a data entry's title, false otherwise.
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*/
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private boolean insideEntryTitle = false;
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/**
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* Receive notification of an opening XML tag: push the tag to
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* <code>xmlTags</code>. If the tag is a title tag inside an entry tag,
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* turn <code>insideEntryTitle</code> to <code>true</code>.
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*/
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@Override
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public void startElement(String uri, String localName, String qName,
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Attributes attributes) throws SAXException {
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if (qName.equals("title") && xmlTags.peek().equals("entry")) {
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insideEntryTitle = true;
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System.out.print("Item " + ++itemNo + ": ");
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}
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xmlTags.push(qName);
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}
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/**
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* Receive notification of a closing XML tag: remove the tag from teh stack.
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* If we were inside of an entry's title, turn <code>insideEntryTitle</code>
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* to <code>false</code>.
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*/
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@Override
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public void endElement(String uri, String localName, String qName)
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throws SAXException {
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// If a "title" element is closed, we start a new line, to prepare
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// printing the new title.
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xmlTags.pop();
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if (insideEntryTitle) {
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insideEntryTitle = false;
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System.out.println();
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}
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}
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/**
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* Callback method for receiving notification of character data inside an
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* XML element.
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*/
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@Override
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public void characters(char[] ch, int start, int length)
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throws SAXException {
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// display the character data if the opening tag is "title" and its parent is
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// "entry"
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if (insideEntryTitle) {
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System.out.print(new String(ch, start, length));
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}
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}
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}
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}
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